Frogs tune call to hole

A Bornean frog tunes its high-pitched call to exploit the acoustics of its tree-hole home and boost its chances of attracting females1.

"The frogs sample the acoustic properties of their holes," says Björn Lardner of the Field Museum of Natural History in Chicago. When they hit a certain note, the call becomes twice as loud, find Lardner and his colleague Maklarin bin Lakim of the Sabah Parks Research and Education Division in Malaysia.

The two-centimetre-long frog Metaphrynella sundana can be heard up to 50 metres away in dense forest. Singing in a hole should dampen the mating call. To investigate, Lardner and Lakim put a male frog into a plastic cylinder containing water.

The animal changed pitch erratically until it hit on the note that matched the resonant properties of the container and amplified its call. When the duo added or removed water from the cylinder, the frog again tried out different songs before settling on a more appropriate note.

“It is better to be super-sexy for a shorter time than 'Mr. Average' for a longer time”

Björn Lardner Field Museum of Natural History, Chicago

When a frog hits the acoustic sweet spot of its arboreal abode, it sings louder and with fewer gaps between calls. The extra effort may mean that it can't sing for as long each night, Lardner suspects, but it probably doesn't matter. "It is a better strategy to be super-sexy for a shorter time than 'Mr. Average' for a longer time," he says.

Some crickets and burrowing frogs sculpt their burrows to amplify their songs. But the tree frog is the first example of an animal adapting its call to take best advantage of existing acoustics, says Lardner.